1. Field of the Invention
This invention relates to a method of supporting a rotary portion in a magnetic disk apparatus.
2. Description of the Prior Art
In a conventional magnetic disk apparatus, a plurality of magnetic disks are fitted to a spindle in a lamination state and the spindle is supported by ball bearings at two positions. A motor is formed of a rotor of a permanent magnet disposed at one end of the spindle and a stator core disposed on a housing and is driven at a predetermined number of rotation. A magnetic fluid seal is provided between the ball bearings and the magnetic disk to prevent contamination of the magnetic disk by lubricating oil of the ball bearings. Balancers are fitted to both ends of the spindle to correct any imbalance of the rotary portion.
Incidentally, apparatuses of this kind are disclosed in japanese Patent Laid-Open Nos. 137765/1987 and 239466/1987.
The prior art described above uses the ball bearings to support a rotating member. Ball bearings having extremely high accuracy are required for the magnetic disk. In the case of the ball bearings, damages or scratches of an outer or inner race, non-uniformity of each ball and eccentricity of a rolling surface are unavoidable and oscillation occurs with these factors as an exciting force. If the natural frequency of the rotation system resonates with this exciting force or its n-times component, great oscillation occurs in the rotation system and contact between the magnetic disk and a slider equipped with a magnetic head is impeded, causing abnormality in recording and reproduction of information.
When the information on the magnetic disk is read or recorded at the timing of seeking, a head assembly does a seeking operation in a track direction and at this time, secondary bending oscillation of the shaft system is excited by seek reaction, causing oscillation and track error.